1-Hydroxy-9-keto-3-alkyl-7,8,9,10-tetrahydro-6H-dibenzo[b,d]pyrans (preferably named as 1-hydroxy-3-alkyl-6,6a,7,8,10,10a-hexahydro-9H-dibenzo[b,d]pyran-9-ones) were synthesized as intermediates by Fahrenholtz, Lurie and Kierstead, J. Am. Chem. Soc., 88, 2079 (1966), 89 5934 (1967) according to the following reaction procedure: a 5-alkyl resorcinol is reacted with diethyl .alpha.-acetylglutarate to form an ethyl 4-methyl-5-hydroxy-7-alkylcoumarin-3-propionate. Cyclization of this lactone ester with a metal hydride yields a tricyclic keto lactone of the following structure (I): ##STR1## Protection of the 9-keto group by ketal formation followed by treatment of the ketal with a methyl Grignard Reagent and subsequent cyclization and removal of the ketal group yields a 1-hydroxy-3-alkyl-6,6-dimethyl-6,6a,7,8-tetrahydro-9H-dibenzo[b,d]pyran-9- one of Formula II below: ##STR2## Reduction of the .DELTA..sup.10(10a) double bond with lithium in liquid ammonia at -78.degree. C. yields predominantly the trans ketone, dl-trans-(1-hydroxy-3-alkyl-6,6-dimethyl-6,6a,7,8,10,10a-hexahydro-9H-dibe nzo[b,d]pyran-9-one) Formula III, along with minor quantities of the corresponding 6a,10a-cis isomer. ##STR3## No pharmacological activity was reported for this compound and it was used only as an intermediate. Compounds according to Formula III can readily be transformed by treatment with a methyl Grignard Reagent to the corresponding 9-methyl-9-hydroxy compound dehydration of which yields directly either a .DELTA..sup.8 or .DELTA..sup.9 -tetrahydrocannabinal derivative, the latter being an active constituent of hashish. The Fahrenholtz et al. synthesis is also described in U.S. Pat. No. 3,507,885 (Fahrenholtz II) and in U.S. Pat. No. 3,636,058 (Fahrenholtz II), a continuation-in-part of the previous patent. (In the Fahrenholtz patents, structure VI corresponds to Formula I above, structure VII to Formula II above, and structure III to Formula III above). Although apparently only a single compound of Formula III above was actually prepared by Fahrenholtz (the 3-n-pentyl derivative -- see Example 8 of Fahrenholtz II), a large number of alkyl substituted resorcinols are described, all of which can be used to synthesize other 3-alkyl derivatives of Formula III. Resorcinols named include 5-(1,2-dimethylheptyl)resorcinol, 5-(1-methyloctyl)-resorcinol, 5-(1-methylhexyl)resorcinol, 5-(1,2-dimethylbutyl)resorcinol, etc. A review article "Problems of Drug Dependence -- Cannabis (Marijuana) Selected Bibliography (1950-1967) prepared by the Medical Literature Branch, Bureau of Medicine, FDA, Department of Health, Education and Welfare, Addendum I, Substances Occurring Naturally in Marijuana, etc., Isbel, (Washington, D.C., 1968)" and an article entitled Recent Advances in the Chemistry of Hashish, Mechoulam and Gaoni, Fortschritte Der Chemie Organicher Naturstoffe, 25, 175 (Springer, Wein, 1957) mention the Fahrenholtz, et al. synthesis as well as other synthetic procedures for preparing active tetrahydrocannabinols; no pharmacological activity for compounds having a ketone ring group at 9 in the dibenzopyran ring system is recorded therein. Two references, U.S. Pat. No. 3,873,576 to Petrzilka and Fahrenholtz I disclose in Examples 11 and 16 respectively, 3-n-pentyl-6,6,9-trimethyl-6a,7,9,9,10,10a-hexahydro-6H-dibenzo[b,d]pyran- 1,9-diol. Fahrenholtz I discloses a 6a.beta.,10a.beta. or cis derivative whereas Petrzilka discloses a trans derivative. Both patents disclose and claim broadly 3-(C.sub.1 -C.sub.10) alkyl derivatives (Claim 11 of Petrzilka and claim 15 of Fahrenholtz I) but the alleged utilities are as intermediates for the preparation of .DELTA..sup.9 -THC (Fahrenholtz I) or as psychomimetic agents, secatives and analgesics (Petrzilka) (Note: Petrzilka, col. 4, lines 63-65 states that the utility of the 1,9-dihydroxy 6,6,9-trimethyl-3-alkyl-hexahydrobenzo[b,d]pyrans of Formula 7 have the same utility as the compounds of Formula I given in Col. 5, lines 47-49). No mention is made in either patent of hypotensive activity. 1,9-Dihydroxy-3-alkyl-6a,7,8,9,10,10a-hexahydro-6H-dibenzo-[b,d]pyrans have not hitherto been prepared.